1. Field of the Invention
The present invention relates to a polymer precursor excellent in transparency with respect to an electromagnetic wave in an ultraviolet range. Particularly, the present invention relates to a polymer precursor, a polymer compound derived from the polymer precursor and a resin composition containing the polymer precursor which can be suitably utilized as material of a product or member formed through a patterning process by an electromagnetic wave, for instance, a forming material of optical goods or optical parts, an insulating material, a layer forming material or an adhesive or the like, and an article produced with the use of the polymer precursor, the polymer compound or the resin composition.
Suitably, the present invention relates to a polyimide precursor excellent in transparency with respect to an electromagnetic wave in an ultraviolet range. Particularly, the present invention relates to high transparency polyimide precursor which can be suitably utilized as material of a product or member formed through a patterning process by an electromagnetic wave, for instance, a forming material of optical goods or optical parts, an insulating material, a layer forming material or an adhesive or the like and is excellent in heat resistance and transparency after imidization. Further, the present invention relates to high transparency polyimide derived from the high transparency polyimide precursor, a resin composition containing the high transparency polyimide precursor and an article produced with the use of the high transparency polyimide precursor, the high transparency polyimide or the resin composition.
2. Description of the Related Art
Polymer material is used for various familiar products due to its properties such as high processability, lightness in weight or the like. Polyimide developed by DuPont, U.S., in 1955 has been further developed so as to apply to an aerospace field or the like because of its excellent heat resistance. Since then, in detailed studies done by many researchers, it was found that properties such as heat resistance, dimensional stability, insulating property and the like are good among organic matters showing top-class properties, hence, polyimide has been applied not only to the aerospace field but also to an insulating material of electronic parts and the like. Nowadays, polyimide is increasingly utilized as a chip coating layer of a semiconductor element, a substrate of a flexible printed-wiring board and the like.
Also, in recent years, in order to solve problems of the polyimide, compounds having a similar engineering process as the imidazole such as polybenzoxazole having low water absorption rate and low permittivity, polybenzimidazole excellent in adhesion property to a substrate and the like are vigorously researched.
Polyimide is a polymer which is synthesized from diamine and acid dianhydride. Precursor of polyimide (polyamic acid) is obtained by reacting diamine and acid dianhydride in liquid. Then, polyimide can be obtained through a dehydration and ring-closure reaction. Generally, since polyimide is poor in solubility to a solvent and difficult to process, polyimide is often obtained by making its precursor, which is polyamic acid, into a desired form followed by heating. Polyamic acid often decomposes by heat or water, thus, it is not good in storage stability. Taking the point into consideration, polyimide, which is improved in such a manner that a skeleton excellent in solubility is introduced to a molecular structure to obtain polyimide so as to be able to dissolve the polyimide into a solvent to form or apply, has been developed. However, this polyimide tends to be inferior in chemical resistance or adhesion to a substrate to the polyimide obtained by the means using a precursor. Hence, either means using a precursor or means using solvent-soluble polyimide is used in accordance with the purpose.
Also, with the advancement of technology, there has been demand for patterning polyimide in a desired form. Hence, polyimide which is capable of pattern forming through processes such as exposure, development and so on using an electromagnetic wave such as ultraviolet ray or the like has been developed. Several means are proposed for patterning polyimide. One of them is a method to obtain a pattern of polyimide in such a manner that patterning is performed in a state of polyimide precursor followed by imidization with thermal treatment or the like. Another method is to obtain a pattern in such a manner that a resist pattern is formed on polyimide itself by organic matters, metals or the like, opening of the resist pattern is treated with a solvent such as hydrazine, inorganic alkali, organic alkali or the like, an organic polar solvent or a mixture thereof to decompose or elute.
The former has an advantage that it is excellent in processability by using a precursor excellent in a solvent solubility. The latter has an advantage that an imidization process which requires a thermal treatment at high temperature or the like is not necessary after pattern forming. The former and the latter are used in accordance with required use thereof.
In the area of semiconductor which has been achieved remarkable development from the last half of the 20th century, presently, polyimide of a type utilizing a precursor capable of patterning is mainly used since, as one reason, polyimide is formed on a silicon wafer substrate, the substrate can tolerate a thermal treatment of high temperature at 300° C. to 400° C. required for imidization.
As means for polyimide patterning of a type utilizing a precursor, various means are proposed. Representative means thereof can be classified broadly into the following two categories:
(1) a means in which a photosensitive resin layer is formed on a surface of a polyimide precursor and the polyimide precursor is patterned by a pattern of the photosensitive resin as the polyimide precursor itself does not have patterning ability; and
(2) a means of pattern forming by an effect of introducing a photosensitive portion to a polyimide precursor itself by bonding or coordinating, a means of pattern forming by an effect of a photosensitive component in a resin composition which is a polyimide precursor mixed with the photosensitive component, and further, a means of a combination of introducing the photosensitive portion and mixing the photosensitive component.
As a representative means of the above (1) group, there is a means of obtaining a polyimide pattern in such a manner that utilizing solubility of polyamic acid, which is a polyimide precursor, to an alkali solvent, on a coating layer of the polyamic acid in the alkali solvent, a resist capable of an alkali development is applied followed by irradiation with an electromagnetic wave in a desired form; simultaneously as development of the resist, polyamic acid exposed from opening of the resist appeared by the development is also eluted in a developer to form a pattern; and then a resist layer on a surface is peeled by an organic solvent to which the polyamic acid is insoluble such as acetone or the like followed by imidization.
On the other hand, as a representative means of the above (2) group, the following means are proposed:
(a) a means of obtaining a polyimide pattern in such a manner that pattern forming is performed by mixing polyamic acid, which is a precurso2r of polyimide, with a naphthoquinonediazide derivative, which functions as a dissolution inhibitor before exposure of an electromagnetic wave and as a dissolution promoter after exposure to produce carboxylic acids, so as to enlarge contrast of dissolution rate of an exposed part and that of an unexposed part with respect to a developer; and imidization is performed;
(b) a means of obtaining a polyimide pattern in such a manner that pattern forming is performed by mixing polyamic acid, which is a precursor of polyimide, with a compound which is a basic substance exhibiting catalytic activity of imidization by exposure of an electromagnetic wave such as a nifedipine derivative or the like followed by heating at an appropriate temperature after exposure so that an exposed part is subject to partial imidization due to the effect of the basic substance produced on the exposed part, and thereby lowering solubility of the exposed part with respect to a developer so as to enlarge contrast of dissolution rate of the exposed part and that of an unexposed part with respect to the developer; and imidization is performed completely;
(c) a means of obtaining a polyimide pattern in such a manner that pattern forming is performed by mixing a polyimide precursor having a skeleton having a radically polymerizable ethylenically unsaturated bond with a photoradical initiator so as to form a cross-linked structure on an exposed part to lower solubility with respect to a developer, and thereby enlarging contrast of dissolution rate of the exposed part and that of an unexposed part with respect to a developer; and imidization is performed;
(d) a means of obtaining a polyimide pattern in such a manner that pattern forming is performed by mixing polyamic acid as a polyimide precursor with a skeleton having a basic part and an radically polymerizable ethylenically unsaturated bond to be bonded ionically; mixing a photoradical initiator thereto to form a cross-linked structure at an exposed part so as to lower solubility with respect to a developer, and thereby enlarging contrast of dissolution rate of the exposed part and that of an unexposed part with respect to the developer; and imidization is performed; and
(e) a means of obtaining a polyimide pattern in such a manner that pattern forming is performed by mixing polyamic acid as a precursor of polyimide with a photoacid (or photobase) generator and a crosslinking agent followed by exposure and heating to proceed crosslinking by the effect of acid (or base) generated by the exposure, and thereby lowering solubility with respect to a developer so as to enlarge contrast of dissolution rate of an exposed part and that of an unexposed part with respect to the developer; and imidization is performed.
The above-mentioned means of (1) group is characterized in that, though the process is more complicated, the degree of freedom of composition of the polyimide precursor to be used is high. Also, impurity other than polyimide is not contained in final polyimide since a photosensitive component or the like is not mixed, hence, the above-mentioned means of (1) group is high in reliability.
On the other hand, the means of (2) group is characterized in that since the polyimide precursor (or the polyimide precursor resin composition) itself has pattern forming ability, the resist layer used in the (1) group is not necessary, hence, process is largely simpler. However, if the polyimide precursor itself does not fully transmit the exposure wavelength, problems may be raised such as decline in sensitivity, not capable of forming a pattern and the like since the electromagnetic wave may not reach the photosensitive component. Therefore, it is necessary to select a skeleton high in transmittance with respect to the exposure wavelength.
In accordance with a demand of the market for forming a finer pattern, shorter exposure wavelength is used gradually shifting from 436 nm to 405 nm or 365 nm. The polyimide precursor used for the above-mentioned means is different in absorption wavelength according to the chemical structure. Generally, the polyimide precursor often has absorption from around 450 nm to the short wavelength side. Particularly, the tendency is strong in a polyimide precursor having many aromatic structures, a part of which or most part of which is in a conjugated state. Also, the polyimide precursor in which efforts are made to make the absorption smaller often has absorption in the wavelength of 400 nm or less. In order to correspond to the exposure at the wavelength of 365 nm or less being capable of a finer process, improvement of transmittance with respect to shorter wavelength has been studied.
Particularly, a polyimide precursor having an aromatic skeleton exhibiting high heat resistance and low coefficient of expansion tends to have absorption in longer wavelength range.
The reason of the absorption of the polyimide precursor is said to be charge transfer. Recently, it is reported that particularly charge transfer in a molecule is highly related to coloring (Polymer Preprints, Japan 48 [5] 939 (1999)). That is, a polyimide precursor which has absorption in shorter wavelength range can be formed by eliminating the charge transfer in the molecule. Based on this principle, as conventional means to shift absorption of the polyimide precursor to shorter wavelength, two major means are proposed.
One means is to shift absorption to shorter wavelength by introducing an aliphatic structure, particularly an alicyclic structure, to a polyimide precursor skeleton in which there are normally many aromatic skeletons to disconnect conjugation of π electron in the skeleton so as to inhibit charge transfer in the skeleton. Particularly, it is disclosed to be effective to introduce an alicyclic skeleton to diamine which is a starting material (Polymer Preprints, Japan 48 [5] 939 (1999), and Japanese Patent Application Laid-Open (JP-A) No. Hei. 10-310639).
The other means is to provide transparency by introducing fluorine in a polyimide precursor skeleton so as to hinder charge transfer in an electronic state of the skeleton (JP-A No. Hei. 05-1148).
As for a polyimide precursor using 2,2′,6,6′-biphenyltetracarboxylic dianhydride as an acid component, Goin et al., U.S., discloses in POLYMER LETTERS Vol. 6, p. 821-825 (1968) that after refining polyamic acid obtained by reacting 2,2′,6,6′-biphenyltetracarboxylicdianhydride with 4,4′-diamino diphenyl ether in dimethylacetamide by reprecipitation using diethyl ether, polyamic acid liquid obtained by being dissolved again in dimethylacetamide is cast followed by heating gradually up to 300° C., and thus obtained polyimide. The thermally decomposing temperature of polyimide is merely disclosed herein, and other physical properties are not stated in detail.
Also, JP-A No. Sho. 56-52722 similarly discloses to utilize polyimide synthesized by using 2,2′,6,6′-biphenyltetracarboxylic dianhydride and 4,4′-diaminodiphenylether as a liquid crystal orientation layer, however, an ability to orient a liquid crystal is merely disclosed herein, and other physical properties are not disclosed.
In Example of JP-A No. Hei. 6-41205 polyimide using 2,2′,6,6′-biphenyltetracarboxylic dianhydride is disclosed, however, the polyimide is used as a protective layer which prevents polymers from adhering to a polymerization container. It is mentioned about a primary coloring of the polymer produced in the polymerization container having the protective layer provided, however, physical properties of polyimide precursor are not stated at all.
JP-A No. Hei. 6-329799 discloses a method for producing a molded body of polyimide and 2,2′,6,6′-biphenyltetracarboxylic dianhydride is mentioned as one representative example of a starting material, however, compound names are merely listed without actual synthesis examples, thus, no specific physical property can be learned.
JP-A No. Hei. 11-140181 discloses method for producing polyimide microparticles and 2,2′,6,6′-biphenyltetracarboxylic dianhydride is mentioned herein as a representative example of a starting material, however, compound names are merely listed without actual synthesis examples, thus, no specific physical property can be learned.
JP-A No. 2002-60489 discloses polyimide and an adhesive tape obtained using the same. 2,2′,6,6′-biphenyltetracarboxylic dianhydride is also mentioned herein as a representative example of a starting material, however, compound names are merely listed without actual synthesis examples, thus, no specific physical property can be learned.
JP-A No. Hei. 3-275725 discloses a method for producing a photoconductive polymer. 2,2′,6,6′-biphenyltetracarboxylic dianhydride is also mentioned herein as a representative example of a material, however, compound names are merely listed without actual synthesis example, thus, no specific physical property can be learned.